The present invention relates to the manufacture of foundry cores or molds, and more particularly to a method and apparatus for manufacturing foundry cores or molds by the integration of a mass of particles, such as sand, into hardened accurately dimensioned forms by means of a catalystresin system distributed on the respective particles in the mass.
In recent years the cold-curing process of making foundry cores has come into wide use in foundry operations. Basically, this process involves mixing separately two volumes of sand or other particulate matter, one with a liquid catalyst-polymerizabe resin or binder, such as a Furfuryl alcohol-derived binder, and the other with a liquid catalyst, such as a mixture of phosphoric and sulfuric acids, until each particle is coated with a film of the resin or catalyst. These two separate sand mixtures are thoroughly mixed or integrated together and deposited in a core box or mold, wherein the catalyzed hardening reaction initiated by the combining of the resin with the catalyst continues until the combined sand mixture hardens into a shaped, substantially integral mass suitable for use as a core or mold in subsequent foundry casting operations.
Unfortunately, this otherwise highly useful method of forming foundry cores or molds suffers several inherent shortcomings. Since hardening of the catalyst-binder film commences instantly as the separate binder and catalystcoated coated sand mixtures are combined, the curing or hardening of the combined sand mixture undergoes at least some progress during the time required to complete the combining operation and before the catalyzed-resin sand mixture is actually forced or placed into the core mold. It is recognized that the greater the extent of the advancement of the hardening of the catalyzed-resin sand mixture prior to its coming to rest in the core box, the weaker will be the resulting core or mold. Furthermore, such advanced hardening may interfere with the proper functioning of the mixing apparatus utilized to combine the two sand mixes, resulting in incomplete mixing and consequent soft spots or voids in the completed mold, or in undesirable jamming or blockage of the mixing apparatus.
Adoption of less reactive resin-catalyst mixes is not a completely satisfactory solution since the longer period of time required of such mixes to set or harden necessitates a longer residence time in the core box, necessitating a greater number of core boxes and a larger storage capability. In high volume production operations, particularly those involving the manufacture of large or complex cores or molds, such requirements often cannot be met without destroying the economic viability of the core or mold forming operation. A more satisfactory solution is to shorten the transit time in the mixing apparatus so that a minimum of hardening of the combined sand mix takes place prior to the combined sand mixture being forced into the core box. Unfortunately, previous attempts at reducing transit time have not been entirely satisfactory, since they have failed, particularly when producing larger sized cores, e.g. above 100 pounds, to achieve the throoughness of mixing of the resin and catalyst sand mixes necessary to consistently obtain cores or molds of uniform hardness and dimensional accuracy. Furthermore, the apparatus for such prior art attempts have not been readily adaptable to forming cores in a wide range of sizes, preventing the use of one machine for forming both large and small cores, e.g. cores from five pounds to five hundred pounds. The co-pending application of Brown et al., Ser. No. 569,827, filed April 21, 1975, and assigned to the present assignee. is directed to apparatus for forming foundry cores or molds which continuously and thoroughly combines the resin and catalyst sand mixes while requiring minimum transit time to economically produce cores or molds having a wide range of sizes. The present application is directed to such an apparatus wherein pressurized staging hoppers are provided for improved dispensing of the catalyst and resin coated sand mixes.
Accordingly, it is a general object of the present invention to provide a new and improved apparatus for forming foundry cores.
It is another object of the present invention to provide a new and improved apparatus for forming foundry cores at high production rates which provides cores of uniform and consistent hardness and dimensional accuracy.
It is a further object of the present invention to provide a new and improved apparatus for manufacturing foundry cores by means of the cold-curing process whereby the resin and catalyst sand mixtures are combined with improved thoroughness and reduced transit time to obtain cores having improved hardness and consistency.
It is a further object of the present invention to provide apparatus for making foundry cores or molds in a wide range of sizes, e.g. of five pounds to five hundred pounds or more, with slow, fast, or very fast hardening binder-catalyst systems.
It is a further object of the present invention to provide apparatus with which, even in the production of large cores and molds, e.g. cores and molds about twentyfive pounds, and especially above one hundred pounds, a highly reactive sand-binder-catalyst system or a highly reactive sand system having substantially zero bench life can be used, and in which each increment of the highly reactive sand mix is virtually instantaneously placed in the desired position in the core box or mold pattern.
It is a further object of the present invention to provide apparatus for making foundry cores or molds in which highly reactive catalyzed mix of particulate material, such as sand, can be continuously prepared and virtually instantly deposited in a shaping element such as a core box or mold pattern, with such speed that the binder-hardening reaction has undergone little, if any, advancement prior to the placement of each respective increment of the particulate material in its ultimate situs in the shaping element.
It is a further object of the present invention to provide apparatus with which respective particles of a reactive catalyzed sand-binder mixture are maintained in highly dispersed but thoroughly intermingled condition until the particles are deposited at their ultimate situs in a mass shaping element, at which situs the particles are packed in an intermingled condition in direct contact with each other to form a shaped mass capable of hardening and becoming self-supporting in a very short period of time.